490 PLIOCENE MOLLUSCA. 



500 to 1000 feet at a certain stage of the Coralline Crag period, I am not aware 

 that any evidence has been adduced in confirmation of such a view. The occasional 

 occurrence of drifted specimens of a few deep-sea forms in a current-bedded 

 deposit can be otherwise explained. 



As is well known, the general facies of the Coralline Crag fauna is distinctly 

 southern. Of the species still living most are now found in the Mediterranean or 

 along the western coasts of France and rortugal,^ while characteristically northern 

 species are as a rule conspicuous by their absence. These facts point, I think, to 

 the view that free communication then existed between the Crag basin and the 

 Atlantic, but not with northern seas. 



The English Crag deposits may have originated in two ways — first, as sub- 

 marine banks, in a sea of no great depth, under the influence of currents, and 

 next as littoral drift, the one representing the conditions attending the deposition 

 of the Coralline Crag, the other those under which recent shell-beaches and sand- 

 banks are now being formed in Holland on the one hand, and those of the Pliocene 

 Red Crag on the other. One case of the former kind, to which Jeffreys called 

 attention, is that of the Turbot Bank off the coast of Antrim, in Ireland, which 

 stretches from the entrance to Belfast Lough towards the Copeland Isles, and lies 

 at a depth of from 25 to 30 fathoms below ordnance datum. It rests against the 

 shore, extending seawards for a short distance and then shelving into deeper water.' 

 The coast of Antrim is separated from Scotland by a narrow channel, through which 

 currents run with great velocity. No deposition takes place there, but shells are 

 swept up from some adjacent sea-bottom and deposited in a spot which is compara- 

 tively sheltered. Most of the mollusca of the Irish Sea live at a depth of less than 

 50 fathoms, except Isocardia cor, a mud-loving species, rare in the Coralline Crag, 

 which gives its name to the Casterlien of Belgium, a deposit, as urged above, 

 synchronous with it, which M. Van den Broeck considers to represent a sea- 

 bottom, undisturbed by currents, in which lamellibranchiate mollusca are found 

 with both valves united and in the position of growth. 



The recorded exposures of Coralline Crag arrange themselves along a curved 

 line, extending in a S.W. — N.E. direction for about 25 miles from Tattingstone, 

 near Ipswich, to Aldeburgh in Suffolk, with a submerged continuation to 

 Thorpe and Sizewell to the north of the latter place. The largest group of 

 these exposures is that between Gedgrave marshes and Aldeburgh, which is 

 narrow and elongate, about 12 miles in length and 2 in width. A map showing 

 the position of the various sections and borings at that time available was 

 published by me in 1898," and is reproduced, by consent of the Council of the 



' Many Coralline Crag species, moreover, are to be found in the Pleistocene deposits of Calabria 

 and Sicily. 



2 Quart. Jo urn. Greol. Soc, vol. liv, p. 326, fig. 4. 



